Electrostatic recording materials

ABSTRACT

AN ELECTROSTATOGRAPHIC RECORDING MATERIAL COMPRISING A NONCONDUCTIVE SUPPORT HAVING THEREON A MEMBER SELECTED FROM THE GROUP CONSISTING OF A PHOTOCONDUCTIVE INSULATING LAYER OR AN ELECTRO-INSULATING LAYER, CHARACTERIZED IN THAT A LAYER HAVING A LOW ELECTRIC RESISTANCE COMPRISING A MEMBER SELECTED FROM THE GROUP CONSISTING OF POLYVINYLBENZENE SULFONIC ACID AND A WATER-SOLUBLE SALT THEREOF IS INTERPOSED THEREBETWEEN.

United States Patent 3,574,682 ELECTROSTATIC RECORDING MATERIALS Satoru Honjo and Yoji Tsuneoka, both of 210 Nakanuma,

Minami-Ashigara-machi, Ashigara-Kamigun, Kanagawa, Japan N0 Drawing. Filed Apr. 11, 1968, Ser. No. 720,443 Claims priority, application Japan, Apr. 12, 1967,

Int. Cl. G03c 1/82 US. Cl. 117-215 3 Claims ABSTRACT OF THE DISCLOSURE An electrostatographic recording material comprising a nonconductive support having thereon a member selected from the group consisting of a photoconductive insulating layer or an electro-insulating layer, characterized in that a layer having a low electric resistance comprising a member selected from the group consisting of polyvinylbenzene sulfonic acid and a water-soluble salt thereof is interposed therebetween.

BACKGROUND OF THE INVENTION The present invention relates to electrostatic recording materials. Electrostatic recording materials according to the present invention refer to the recording materials employed for electrostatic recording in a broad sense (electrostatography), i.e., recording in the field comprising both electrophotography and electrostatic recording in a narrow sense (electrography).

For instance, in the case of electrophotography, an electrophotographic material comprising a photoconductive layer provided on a conductive support is normally used in the following manner. The photoconductive layer of said material is charged in the dark and the charged layer exposed imagewise to form an electrostatic latent image corresponding to the pattern of the remaining charges, which is then developed by causing properly charged toners to stick thereto in the dark. Where the charge of the toner is opposite to that of the electrostatic latent image, toner sticks only to the areas of higher potential which have not been exposed to light. As toners can usually be melted by heat, the above-mentioned toners sticking to the electrostatic latent image can be fixed by subsequent heating thereof.

To obtain a toner image of excellent quality, it is an extremely important requirement that at the time of exposure of a recording material after the charging thereof, those portions of photoconductive layer of said material which are exposed to light promptly discharge upon exposure to light. Delay in discharge or incomplete discharge causes an obscure image as well as fogging. Where it is desired to produce an image of continuous gradation, the quality of image obtained will be extremely poor unless the potential of the supoprt immediately after charging is entirely uniform. For this reason, it is necessary that the conductivity of the support be considerably high.

The first step in the formation of electrostatic latent image in the above-mentioned electrophotography, that is, the process of charging a recording material, is also carried out in the case of electrostatic recording and is the image forming step itself in the latter case. Uniform charging of a certain required area of the electrostatic recording 3,574,682 Patented Apr. 13, 1971 material is quite important to obtain an image of excellent quality. For that purpose it is likewise necessary that the inner layer contiguous to the insulative recording layer of recording material be conductive.

Accordingly, these desirable conditions exit in the case where the supporting material is made of metal. In the case, for instance, of paper, cloth or wood used as a supporting material, such supporting material should be made conductive. For instance, when using a recording material which utilizes such material as the supporting material, satisfactory results can be obtained under conditions of high humidity, but if relative humidity is below 40%, the supporting material tends to be dry and reduced in conductivity, its effect being thus deteriorated. To solve these problems, the wetting of electrostatographic material prior to use or impregnation of a support with a hygroscopic salt or charging preveutives such as a polymeric material containing a quaternary ammonium radical in its recurring unit structure, or various other means have been proposed in the past.

However, impregnating with a hygroscopic substance is a complicated process and is subject to the danger of such hygroscopic substance staining the insulative recording layer. The method of adding a charge preventing agent to the support is quite excellent in that it can fully reduce electric resistance. Also, such agent does not penetrate into the coated layer provided on the support. But, if it is coated over a porous support such as cloth, paper or wood, such film, if additional amounts of an organic solvent is further coated thereon it, cannot fully prevent said solvent from penetrating into the support.

The use of a mixture comprising polyvinyl alcohol possessing high permeation interrupting capacity as a medium has been proposed. However, even this method was insufficient to eliminate the above-mentioned defects. If a base paper serving as a support is processed with polyvinyl alcohol, etc., and thereafter by means of a polymer product containing a quaternary ammonium radical, relatively satisfactory results can be obtained. However, the processing of the supporting material takes time and the production costs of the recording material is thus increased and in addition, maintaining uniform characteristics of the products is quite difiicult.

The present invention aims to solve these problems and the object is to provide a novel electrostatic recording material usable over a wide range of humidity conditions at normal temperatures (generally 0 to 30 C.). The invention is especially applicable in cases where a supporting material to be provided with electrophotographic insulative layer or electrostatographic insulative layer is substantially insulative, i.e., the invention provides it with conductivity. The present invention consists in providing a novel layer processed and rendered conductive and possessing desirable characteristics in that an insulative electrostatographic layer is provided on a support which gives no deleterious results where organic solvents are employed.

BRIEF DESCRIPTION OF THE INVENTION That is, the present invention relates to a recording material and a process for its preparation being characterized in that in the electrophotographic or electrostatographic material comprising the photoconductive insulative layer or an electric insulative layer provided on a non-conductive supporting material such as paper, cloth or wooden material, a low electric resistance layer has as its main constitutent polyvinyl benzene sulfonic acid or a water soluble salt thereof provided between the supporting material and the insulative layer.

DETAILED DESCRIPTION OF THE INVENTION Under the present invention, polyvinyl benzene sulfonic acid or its water soluble salt is employed as a conductive processing agent for a nonconductive supporting material. Polyvinyl benzene sulfonic acid itself is hydrophilic, but it is required to be soluble especially in an aqueous solvent (including water). Therefore, it is desirable that its polymerization degree not be high. In the case of water soluble salts, their polymerization degree is desirably such that the viscosity of their aqueous solutions at a pH in the range of from 6 to 7 is about 50-500 c.p.s. at normal temperatures. The use of such water soluble salts of this vinyl polymer such as the sodium, potassium or ammonium salts is recommended because of their high solubility in water.

In addition to polyvinyl benzene sulfonic acid or its Water soluble salt, glycerine, diethylene glycol, triethylene glycol, pentaerythritol or mannitol, etc., may be blended as required as a plasticizer. If these substances are blended, high conductivity seems to be ensured over a wide humidity range. Since polyvinyl benzene sulfonic acid or its salts are possessed of superior film-forming properties, incorporation of the abovementioned polyhydric alcohols in larger amounts does not result in a deterioration of the solvent hold-out properties of the resulting layer. Accordingly, aeration can be realized as compared with methods wherein the sub-coating must be applied twice.

It offers another advantage in that the coated film is small in thickness. However, if another polymer such as polyvinyl alcohol, etc., is added to polyvinyl benzene sulphonate, in case of low humidity, the insulative property is increased according to the volume so added. Therefore, excessive addition is not desirable. Accordingly, in the case of adding a relatively high-resistance polymer to polyvinyl benzene sulphonate, it should be limited to a maximum of 40% of the total film components. Applicable as other blending components are hygroscopic inorganic salts and inorganic pigments, etc.

The processing method of the present invention may be applied to the entire interior or base paper, for instance, impregnating the Whole paper with the sodium salt of polyvinyl benzene sulfonic acid. Due to the strong solvent permeation preventive effect of the sodium salt of polyvinyl benzene sulfonic acid soda, its application as an intermediate layer can be said to be a preferable mode of application.

As the sodium salt of polyvinyl benzene sulfonic acid forms a relatively hard film, for practical application of the present invention, it is desirable to add 70-3O parts (by weight) of water soluble liquid or soft solid polyhydric alcohol etc., as a plasticizer to 30-70 parts (by weight) of sodium polyvinyl benzene sulphonate. Further, if required, film forming components lower in conductivity may be included in a volume of less than 80% of said polymer. The addition of these components prevents the recording material from being curled and moreover, can completely prevent the permeation of solvent.

The present invention brings about an especially advantageous result in the case where a porous supporting material such as paper, cloth or wood etc., is employed and an organic solvent is used as a solvent for photoconductive insulative layers or electric insulative layers. That is, the important effect of the present invention consists in the solution of problems in the case of production of recording materials, as a result of which liquid applied to provide a photoconductive layer on a recording material does not permeate into the interior of the supporting material. Therefore, the present invention has a great advantage that in the electrostatic recording in a broad sense, even if the supporting medium of recording material were a non-conductive material, uniform charging of only the required portion of the recording material is possible over a wide humidity range at normal temperature and an excellent recording image not involving any fogging can be obtained.

The present invention will now be described in detail on the basis of the following examples.

Example 1 A liquid composed of 10 parts of the sodium salt of polyvinyl benzene sulfonic acid, 10 parts of glycerine, 60 parts of water and 20 parts of methanol was applied to the surface of so-called machine-coated paper of g./m. in such manner that non-volatile component is coated 2 g.-25 g. per m.

The surface resistance of the paper obtained was measured and found to be 3.2)(10 ohms on a square surface in an atmosphere of RH 35% at 25 C. Under the same conditions, untreated paper showed a resistance of 1.2x 10 ohms/square.

Where a maleic acid-vinyl methyl ether copolymer was employed in place of the sodium salt of polyvinyl benzene sulfonic acid, the resistance of coated paper was 3x10 ohms/ square under the same conditions.

Example 2 Potassium salt of polyvinyl benzene sulfonic acid and a 1:1 mixture of polyvinyl alcohol and glycerine were mixed at various mixture ratios and coated in the form of an aqueous solution on the sheets of art paper in approximately the same quantity and dried. After drying, these sheets were left for a long period of time in an atmosphere of 30% RH at 25 C. and the surface resistance was measured.

The results are shown in the following table,

As will be clear from this table, specimens as far down as No. 3 can display quite excellent characteristics as electrophotographic sensitive material or electrostatic recording material.

In fact, when zinc oxide layer with dispersed resin therein was applied to these sheets, it was found that under the same humidity condition as above, specimens down to No. 3 did not produce any image density irregularities or fogging and could be used advantageously even for the rendering of images of continuous gradation. Specimens No. 4 to No. 6 could be used for the reproduction of linear images.

In the meantime, with respect to the solvent permeation preventive effects of the above-mentioned specimens, scarcely any difference could be found between them.

What is claimed is:

1. In an electrostatographic recording material comprising a non-conductive support having an insulating layer thereon consisting of a photoconductive insulating layer or an electro-insulating layer, the improvement comprising providing a low electric resistance layer selected from the group consisting of polyvinylbenzene sulfonic acid and a water-soluble salt thereof between said non-conductive support and said insulating layer.

2. The electrostatographic recording material of claim 1 wherein said low electric resistance layer contains a plasticizer.

3. The electrostatographic recording material of claim 1 wherein said 10w electric resistance layer further contains a film forming resinous material, said resinous material being present in an amount less than 40% of the total weight of said layer components References Cited UNITED STATES PATENTS 6 Morey 9687 Baer 9687 Guestaux et a1. 9687 Cassiers et a1. 961.5 Nadeau 9687 ALFRED L. LEAVITT, Primary Examiner A. GRIMALDI, Assistant Examiner -U.S. C1. X.R. 

